As reported in previous articles in the Bulletin (see articles from 2010 and 2011), strains of the fungus that causes frogeye leaf spot of soybean, Cercospora sojina, that are resistant to strobilurin fungicides have been observed in the U.S. since 2010.In 2012, soybean samples affected by frogeye leaf spot were collected in Illinois and tested for strobilurin fungicide–resistant strains of Cercospora sojina. In addition, colleagues from other states sent soybean samples to my laboratory for testing. In 2012, several new counties and parishes were found to have resistant strains (see Table 1).

Table 1. Counties and parishes in the U.S. in which strobilurin fungicide-resistant strains ofCercospora sojinahave been detected (2010-2012).